The item "closing walls" has the effect that the size of the field is shrinking. The item "big hole" has the effect that the player doesn't create a line anymore for 6 seconds which makes you immortal. Another effect of "big hole" is the ability to go out of the field and come back.

When the field is shrinking it also takes away space where items spawned. With the item "big hole" you can still collect those items. This is leading me to my question: Do items still spawn at the area that was taken by the item "closing walls" or do they only spawn at the middle area that is left?

The game exists on an infinite plane in which a small area is sourrounded by the walls. These walls build our playfield on the infinite plane. Every curve has a collision body attached to it and the walls have that aswell. When the curves body collides with the wall, it will be detected and stopped (0 speed = looks dead to us). The items are objects that have their own collision body, when a curve collides with this object, it will have certain effects on the game values (speed increase/decrease etc.). These objects (our items) will spawn randomly at certain coordinates on the plane. Most likely the range of these x,y-coordinates are bound to our playfield. When the "closing walls" object is collided with, it will shrink the playfield that is surrounded by the walls. The objects (our items) will still spawn randomly at the x,y-coordinates as they did before. Thus, some items will effectively be outside the playfield now, because the x,y points are not inside the playfield anymore! Therefore, if you now somehow go outside of the walls, you could still collide with these objects (items) and this will result in changing game values.